In integrated circuits, the degree of integration increases more and more. In the manufacture of semiconductor substrates of ULSIs, etc., it has become necessary to undergo processing of hyperfine patterns having a line width of quarter microns or less. As means for making patterns fine, it is known to shorten the wavelength of an exposure light source to be used for the formation of resist patterns.
For example, in the manufacture of semiconductor elements having a degree of integration of up to 64 Mbits, i-rays (365 nm) of a high-pressure mercury vapor lamp have been used as a light source up to date. As a positive-working resist corresponding to this light source, many compositions containing a novolak resin and a naphthoquinone diazide compound as a photosensitive material have been developed, and sufficient results have been produced in fabrication of line widths of about 0.3 μm or more. Further, in the manufacture of semiconductor elements having a degree of integration of 256 Mbits or more, KrF excimer laser beams (248 nm) have been employed as the exposure light source in place of the i-rays.
In addition, for the purpose of manufacturing semiconductor elements having a degree of integration of 1 Gbits or more, in recent years, the use of ArF excimer laser beams (193 nm) and the use of F2 excimer laser beams (157 nm) for the formation of patterns of 0.1 μm or less, both of which are a light source of shorter wavelengths, are being investigated.
Adaptive to shortening of the wavelengths of these light sources, the constitutional components of the resist materials and their chemical structures largely change.
As resist compositions for exposure by KrF excimer laser beams, there have been developed so-called chemically amplified resists that are a composition comprising a combination of, as a major component, a resin having poly(hydroxystyrene) having low absorption in a region of 248 nm as a basic skeleton and being protected by an acid-decomposable group and a compound capable of generating an acid upon irradiation with far ultraviolet rays (photo acid generator).
Further, as resist compositions for exposure by ArF excimer laser beams (193 nm), there have been developed chemically amplified resists using an acid-decomposable resin in which an alicyclic structure not having absorption at 193 nm is introduced into a main chain or side chains of the polymer.
It has become clear that as to F2 excimer layer beams (157 nm), the foregoing alicyclic type resins have large absorption in a region of 157 nm and are insufficient for obtaining the desired patterns of 0.1 μm or less. On the other hand, Proc. SPIE., Vol. 3678, p.13 (1999) reports that resins having a fluorine atom (perfluoro structure) introduced thereinto have sufficient transparency at 157 nm. Structures of effective fluorocarbon resins are proposed in, for example, Proc. SPIE., Vol. 3999, p. 330 (2000), ibid., p. 357 (2000) and ibid., p. 365 (2000), and WO 00/17712, and resist compositions containing a fluorine-containing resin are being investigated.
However, these resins were not satisfactory in transparency at 157 nm and various other properties such as sensitivity and resolving power. Further, these resins involved a problem such that the coating properties are poor.